This invention relates in general to bearing seals and more particularly to seals which have the capacity to sense angular velocity.
Antilock brake systems, which are found on many automotive vehicles of current manufacture, require devices at the wheels for sensing the angular velocities of the individual road wheels. On any vehicle so equipped, the speed sensing devices generate signals which are monitored by an electronic processor that in turn controls the braking forces applied to the wheels, the object being to keep all four wheels rotating at the same velocity, even though one of the wheels may be rolling over a surface that offers considerably less frictional resistance than the surface over which the others are rolling. Some automobiles also have traction control systems that minimize slip at the drive wheels and thereby maximize the tractive effect. These systems rely on speed sensing devices as well, and indeed when a vehicle is equipped with both an antilock braking system and a traction control system, the speed sensing devices at the drive wheels may serve both systems.
The typical speed sensing device includes an encoder ring which rotates with the wheel to which the device is assigned and a sensor which monitors the encoder ring in the sense that it produces a pulsating electrical signal the frequency of which reflects the angular velocity of the ring. To this end, the ring, which is formed from a ferrous metal, has discontinuities in the form of teeth or apertures that disrupt a magnetic flux upon rotation of the ring. The sensor responds to the periodic disruptions and delivers a signal, the frequency of which is proportional to the angular velocity of the ring and vehicle wheel. In order for the sensor to operate effectively, the head of the sensor must be quite close to the rotating ring.
While the typical sensing device is located in the region of the bearing for the wheel that it monitors, it still lies outside the sealed environment of the bearing which is often supplied as a package. As such, the sensing device is exposed to water and much worse corrosive road chemicals. It is also exposed to grit and to stone impingement.
To be sure, others have placed encoder rings within the sealed environments of bearing packages. Indeed, where the inner races of the bearings rotate, as holds true at the front wheels for most front wheel drive automobiles, the bearing assemblies will accommodate speed sensing devices. Sometimes enough space exists between the two rows of rolling elements in such a package to accept an encoder ring which rotates with the inner races, while the outer races or housing in which the outer races fit accommodates the sensor. The sensor head, the encoder ring, and the gap which lies between them all exist within an environment isolated by seals which protect the raceways and rolling elements of the bearing. U.S. Pat. No. 5,085,519 shows such an arrangement.
But when the outer races of the bearing assemblies rotate around stationary inner races, as holds true for some designs used at the nondriven front wheels of rear wheel drive automobiles, the bearing assemblies do not easily accept a sensing device. The problem resides in mounting the sensor and accommodating its electrical leads. Relatively little space exists in the sealed environment for the somewhat bulky sensor, and the spindle must undergo additional machining to provide bores for the leads. For this reason, in most bearing assemblies which have both rotating outer races and sensing devices, the sensors are located outside of the bearing assemblies. In this regard, see U.S. Pat. Nos. 4,884,901 and 4,795,278. While others have attempted to incorporate the sensing devices into the seals, the arrangements are cumbersome and diminish the effectiveness of the seals. Moreover, the sensors are arranged such that they are not easily removed and replaced.
The present invention resides in a seal which contains a speed sensing device, with the encoder ring and the head of the speed sensing device being located in a region isolated from the surrounding environment by the seal. Moreover, the seal has excellent sealing characteristics and accommodates the sensing device such that the sensing device does not significantly enlarge the bearing assembly or render it unacceptable for traditional bearing mountings. The seal comes preassembled, and is designed for use in preassembled bearing packages where the air gap between the encoder ring and the sensor head of the seal are preset. Yet in several embodiments the sensor may be removed quite easily from the seal, should it require replacement.